a. Field of the Invention
This invention relates to backstopping clutches. In particular, the instant invention relates to a backstopping clutch in which a braking torque is transmitted through a radial surface of the outer race to permit improved torque transmission while also reducing the size of the clutch.
b. Background Art
In many motor driven systems, it is desirable to prevent or limit movement of system components in one direction. For example, mining operations typically use inclined conveyors to convey material to a surface location or other outlet. It is desirable to prevent or limit reverse movement of the conveyor in the event of a loss of power or a failure of a driveline component such as a motor, gearbox or coupling in order to prevent material from moving backwards on the conveyor and causing damage to the system and significant injuries to personnel operating the system.
Backstopping clutches are frequently used to prevent reverse rotation of rotating system components. A conventional backstopping clutch 10 as shown in FIG. 1 includes an inner race 12 that is mounted to a shaft (not shown), driven by a motor or similar device, for rotation with the shaft about a rotational axis 14. An outer race 16 is disposed radially outward of the inner race 12 and is fixed against rotation. A plurality of torque transmission members 18 such as rollers or sprags are disposed radially between the inner and outer races 12, 16. Races 12, 16 and/or members 18 are shaped such that when the shaft and inner race 12 are driven by the motor in one rotational direction, members 18 assume a first position permitting relative rotation of the inner and outer races 12, 16. When the inner race 12 is driven in the opposite rotational direction (e.g. by the force of the load of material upon failure of the motor), members 18 assume a second position and forcefully engage the inner and outer races 12, 16 and prevent the inner race 12 and driven shaft from rotating relative to the fixed outer race 16.
In the clutch 10 shown in FIGS. 1, spring loaded friction discs 20, 22 are disposed on either axial end of outer race 16 between race 16 and the surrounding structure. Braking torque is therefore transmitted through the axial ends of outer race 16. The clutch 10 provides a relatively low-maintenance and simple design, but has several disadvantages. The clutch 10 transmits relatively low braking torque despite the use of a relatively large size clutch. The clutch 10 also has relatively low heat conductivity which limits friction generated through the discs 20, 22. Wear on the discs 20, 22 (as well as thermal expansion and manufacturing tolerances) lead to variable axial loading on the outer race 16 and relatively large changes in the coefficient of friction. The outer race 16 must also be centered using sensitive plane bearings or relatively large roller bearings. The design of clutch 10 also makes it difficult to adapt to various drive trains. Finally, the relatively high heat generated by the clutch limits the time that the clutch can slip which lessens its ability to dampen longitudinal vibrations along a conveyor resulting from a sudden failure of the motor or related components.
The inventor herein has recognized a need for a backstopping clutch that will minimize and/or eliminate one or more of the above-identified deficiencies.